Display Device

ABSTRACT

The display device includes: a flexible display panel including a display portion in which scanning lines and signal lines cross each other; a supporting portion for supporting an end portion of the flexible display panel; a signal line driver circuit for outputting a signal to the signal line, which is provided for the supporting portion; and a scanning line driver circuit for outputting a signal to the scanning line, which is provided for a flexible surface of the display panel in a direction which is perpendicular or substantially perpendicular to the supporting portion.

This application is a continuation of copending application Ser. No.13/684,946 filed on Nov. 26, 2012 which is a continuation of applicationSer. No. 12/769,298 filed on Apr. 28, 2010 (now U.S. Pat. No. 8,319,725issued Nov. 27, 2012), which are all incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a display device.

BACKGROUND ART

In recent years, the mode of providing text data or image data ofnewspapers, magazines, and the like as electronic data has beenincreasingly adopted with the development of technique fordigitalization. This kind of electronic data is featured in that thecontents thereof are viewed with a display device equipped with apersonal computer (PC) and the like.

However, the display device equipped with a personal computer (PC) andthe like significantly differs from the paper media such as newspapersand magazines in that the convenience such as portability is poor.

On the other hand, aiming to solve the above-described difference fromthe paper media, flexible electronic paper has been proposed (forexample, see Patent Document 1). In the case where a display portion ofthe flexible electronic paper is formed using an element such as atransistor, a circuit for driving the transistor needs be provided. Inthat case, bending of the electronic paper might cause breaking of thecircuit. Further, the degree of bending of the electronic paper might belimited by the driver circuit.

PATENT DOCUMENT

-   Patent Document 1: Japanese Published Patent Application No.    2003-337353

DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide adisplay device in which occurrence of breaking of a driver circuit atthe time when a flexible panel is handled is suppressed. An object ofone embodiment of the present invention is to provide a display devicein which the structure is simplified.

One embodiment of the present invention is a display device including: aflexible display panel including a display portion in which scanninglines and signal lines cross each other; a supporting portion forsupporting an end portion of the flexible display panel; a signal linedriver circuit for outputting a signal to the signal line, which isprovided for the supporting portion; and a scanning line driver circuitfor outputting a signal to the scanning line, which is provided for aflexible surface of the display panel in a direction which isperpendicular or substantially perpendicular to the supporting portion.

According to one embodiment of the present invention, a display devicein which a scanning line driver circuit includes a plurality of circuitportions and the plurality of circuit portions are spaced from eachother may be provided.

According to one embodiment of the present invention, a display devicein which a stress concentration region is provided between a pluralityof circuit portions may be provided.

According to one embodiment of the present invention, a display devicein which a scanning line driver circuit and a signal line driver circuiteach includes a transistor and the transistor included in the scanningline driver circuit and the transistor included in the signal linedriver circuit have structures which are different from each other maybe provided.

According to one embodiment of the present invention, a display devicein which a channel layer of a transistor included in a scanning linedriver circuit is a non-single-crystal semiconductor and a channel layerof a transistor included in a signal line driver circuit is a singlecrystal semiconductor may be provided.

According to one embodiment of the present invention, a display devicein which a non-single-crystal semiconductor is amorphous silicon,microcrystalline silicon, polysilicon, or an oxide semiconductor may beprovided.

According to one embodiment of the present invention, a display devicein which a display portion includes a transistor and a channel layerincluded in a transistor included in the display portion and a channellayer included in a transistor included in a scanning line drivercircuit are formed using the same material may be provided.

According to one embodiment of the present invention, a display devicein which a supporting portion is provided with at least one of abattery, an antenna, a CPU, and a memory in addition to a signal linedriver circuit may be provided.

In this specification and the like, a “semiconductor device” indicatesany device capable of functioning by utilizing semiconductorcharacteristics, and electro-optic devices, semiconductor circuits, andelectronic appliances are all included in the category of thesemiconductor device.

Further, in this specification and the like, a “display device” includesin its category a light-emitting device and a liquid crystal displaydevice. The light-emitting device includes a light-emitting element andthe liquid crystal display device includes a liquid crystal element. Thelight-emitting element includes in its category any element whoseluminance is controlled by a current or a voltage; specifically, aninorganic electroluminescent (EL) element, an organic EL element, andthe like can be given as examples thereof.

In accordance with one embodiment of the present invention, a sturdydisplay device with less breaking of a driver circuit can be provided.

In accordance with one embodiment of the present invention, cost of adisplay device can be reduced by simplifying the structure thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate one mode of a display device of the presentinvention.

FIGS. 2A to 2C illustrate one mode of a display device of the presentinvention.

FIGS. 3A to 3C illustrate one mode of a display device of the presentinvention.

FIGS. 4A to 4C illustrate one mode of a display device of the presentinvention.

FIG. 5 illustrates one mode of a supporting portion of a display deviceof the present invention.

FIGS. 6A to 6D each illustrate one mode of a display device of thepresent invention.

FIGS. 7A and 7B illustrate one mode of a display device of the presentinvention.

FIGS. 8A to 8C each illustrate one mode of a display device of thepresent invention.

FIGS. 9A to 9C illustrate one mode of a display device of the presentinvention.

FIGS. 10A to 10C illustrate one mode of a display device of the presentinvention.

FIGS. 11A to 11C each illustrate one mode of a display panel of thepresent invention.

FIGS. 12A and 12B each illustrate one mode of a display panel of thepresent invention.

FIG. 13 illustrates one mode of a display panel of the presentinvention.

FIG. 14 illustrates one mode of a display panel of the presentinvention.

FIGS. 15A to 15D each illustrate one mode of a transistor applicable toa display device of the present invention.

FIG. 16 illustrates one mode of a display panel of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, Embodiments are described in detail using drawings. Notethat the present invention is not limited to the description of theembodiments, and it is apparent to those skilled in the art that modesand details can be modified in various ways without departing from thespirit of the present invention disclosed in this specification and thelike. Structures of different embodiments can be implemented bycombination appropriately. In description of the present inventionhereinafter, the same reference numerals are used for indicating thesame or similar function portions throughout the drawings, descriptionon which is not repeated.

Note that the size, the thickness of a layer, and a region of eachstructure illustrated in the drawings and the like in the embodimentsare exaggerated for simplicity in some cases. Therefore, the embodimentsof the present invention are not limited by those scales.

Note that the numeral terms such as “first”, “second”, and “third” inthis specification are used in order to avoid confusion betweencomponents and do not set a limitation on number.

Embodiment 1

In Embodiment 1, an example of a display device will be described withreference to drawings.

The display device described in Embodiment 1 includes the following: aflexible display panel including a display portion in which scanninglines and signal lines cross each other; a supporting portion forsupporting an end portion of the flexible display panel; a signal linedriver circuit for outputting a signal to the signal line, which isprovided for the supporting portion; and a scanning line driver circuitfor outputting a signal to the scanning line, which is provided for aflexible surface of the display panel in a direction which isperpendicular or substantially perpendicular to the supporting portion.

FIG. 1 illustrates the case where a supporting portion 4308 is providedat an end portion of a display panel 4311. A specific structure of thedisplay device will be described using FIGS. 1A and 1B below. FIG. 1Aillustrates the display device which is horizontally disposed, and FIG.1B illustrates the display device which is vertically disposed.

The display device illustrated in FIGS. 1A and 1B includes the displaypanel 4311 including a display portion 4301, the supporting portion 4308provided at an end portion of the display panel 4311, scanning linedriver circuits 4321 a and 4321 b for controlling display on the displayportion 4301, and a signal line driver circuit 4323 for controllingdisplay on the display portion 4301.

The scanning line driver circuits 4321 a and 4321 b are provided for thedisplay panel 4311 and the signal line driver circuit 4323 is providedinside the supporting portion 4308.

The display panel 4311 may be flexible. In that case, a pixel circuitincluded in the display portion 4301 and the scanning line drivercircuits 4321 a and 4321 b may be provided over a flexible substratesuch as a plastic substrate.

It is preferable that the supporting portion 4308 be less flexible (morerigid) than at least the display panel 4311. For example, a housingforming the supporting portion 4308 can be formed using plastic, metal,or the like which is thicker than the display panel 4311. In that case,the display device can be bent (warped) at a portion other than thesupporting portion 4308.

There is no particular limitation on where to arrange the supportingportion 4308. For example, the supporting portion 4308 can be providedalong an end portion of the display panel 4311. For example, as shown inFIGS. 1A and 1B, in the case where the display panel 4311 has arectangular shape, the supporting portion 4308 can be provided along apredetermined side of the display panel 4311 (so that the side isfixed). Note that the “rectangular shape” here includes a shape in whicha corner of the rectangular is rounded.

The signal line driver circuit 4323 is provided inside the supportingportion 4308. For example, the supporting portion 4308 is formed using acolumnar housing with a hollow or a cylindrical housing with a hollow,and the signal line driver circuit 4323 can be provided in the hollow.When the signal line driver circuit 4323 is provided inside thesupporting portion 4308, damage to the signal line driver circuit 4323due to bending of the display panel 4311 can be prevented.

Further, as shown in FIGS. 1A and 1B, the scanning line driver circuits4321 a and 4321 b are preferably provided at both end portions of thedisplay panel 4311 in a direction parallel or substantially parallel tothe supporting portion 4308. As a result, leading of a wiring can bereduced and the structure can be simplified in comparison with the casewhere the scanning line driver circuit and the signal line drivercircuit are provided at one portion (e.g., the supporting portion 4308).

Further, the scanning line driver circuits 4321 a and 4321 b and thepixel circuit included in the display portion 4301 may be formed over aflexible substrate through the same process, so that the scanning linedriver circuits 4321 a and 4321 b can be bent and cost reduction can beachieved.

The pixel circuit included in the display portion 4301 and the scanningline driver circuits 4321 a and 4321 b each can be formed using a thinfilm transistor or the like. On the other hand, a high-speed operationcircuit such as the signal line driver circuit 4323 can be formed usingan integrated circuit (IC) formed using a semiconductor substrate suchas a silicon substrate or an SOI substrate, and the IC can be providedinside the supporting portion 4308.

When the IC including the high-speed operation circuit such as a signalline driver circuit is provided inside the supporting portion and thescanning line driver circuit and the pixel circuit included in thedisplay portion are formed using elements such as thin film transistorsover a flexible substrate as described above, the display panel can bebent easily, occurrence of breaking of the IC due to the bending of thedisplay panel can be suppressed, and cost reduction can be achieved incomparison with the case where the signal line driver circuit and thescanning line driver circuit are provided using an IC. In addition, whenthe scanning line driver circuit is provided on the display panel at theend portion of the display panel in a direction perpendicular orsubstantially perpendicular to the supporting portion, leading of awiring can be suppressed and the structure can be simplified.

Although the case where the scanning line driver circuit is provided atboth end portions of the display panel 4311 is illustrated in FIGS. 1Aand 1B, the scanning line driver circuit (either one of the scanningline driver circuit 4321 a and the scanning line driver circuit 4321 b)may be provided at one end portion.

Embodiment 1 can be implemented in appropriate combination with anystructure described in the other embodiments.

Embodiment Mode 2

In Embodiment 2, a specific structure of the above-described displaydevice illustrated in FIGS. 1A and 1B will be described using drawings.The structures described in Embodiment 2 are in common with thatdescribed in Embodiment 1 in many points, and thus, in the descriptionbelow, description of the common points will be omitted and differentpoints will be described in detail.

First, an example of the specific structure of the display device isdescribed using FIGS. 2A to 2C. FIG. 2A is a plane view of the displaydevice, FIG. 2B is a cross-sectional view along line A1-B1 of FIG. 2A,and FIG. 2C is a detailed schematic view of the cross section.

As for the display device shown in FIGS. 2A to 2C, the supportingportion 4308 is formed using a housing with a hollow, and the signalline driver circuit 4323 is provided inside the housing. In thisembodiment, the signal line driver circuit 4323 is formed using an IC,and the IC is provided inside the supporting portion 4308. The IC can beformed using an SOI substrate, a semiconductor substrate such as asilicon substrate, or the like. Any circuit (e.g., a CPU, a memory)other than the signal line driver circuit can be provided for the IC aswell.

Further, FIGS. 2A to 2C illustrate the case where the IC provided insidethe supporting portion 4308 is mounted on a flexible printed circuit(FPC) by a tape automated bonding (TAB) method. More specifically, thesignal line driver circuit 4323 for controlling the display portion 4301is provided on an FPC 4324, and the FPC 4324 is electrically connectedto a printed board 4325.

As shown in FIGS. 2A to 2C, the printed board 4325 can be provided to bein contact with the supporting portion 4308.

In the case where the signal line driver circuit 4323 is provided on theFPC 4324, it is preferable to provide a stress concentration region 4326for the display panel 4311. The stress concentration region 4326provided for the display panel makes it possible to reduce the stresswhich is applied to the FPC 4324 at the time when the display panel 4311is bent and to suppress the occurrence of breaking of the signal linedriver circuit 4323 provided on the FPC 4324.

The stress concentration region means a region where a stress formed bydeformation of a material due to cutting or the like, change of thestrength against bending and/or extension due to attachment of amaterial or the like, or the like is concentrated. Specifically, thestress concentration region 4326 can be formed by providing a cutportion (depression or groove) at a portion at which the display panel4311 is bent.

For example, the display panel 4311 can be formed using an elementsubstrate 4331 and a sealing substrate 4332, and one or both of theelement substrate 4331 and the sealing substrate 4332 can be providedwith a cut portion. FIGS. 2A to 2C illustrate the case where the cutportion is provided in the sealing substrate 4332 to form the stressconcentration region 4326. In addition, in the structure described here,the scanning line driver circuits 4321 a and 4321 b and a pixel circuitwhich drives the display portion 4301 can be formed on the elementsubstrate 4331, and these circuits can be electrically connected to theFPC 4324.

In the display portion 4301, pixels are arranged (disposed) in matrix,and scanning lines 4361 and signal lines 4362 are arranged so as todissect at right angles. As for the arrangement of the pixels, thepixels may be arranged either linearly in a longitudinal direction andin a lateral direction or zigzag. Therefore, in the case of stripearrangement or the case where dots for three colors are arranged indelta, the scanning lines 4361 and the signal lines 4362 are arrangeddepending on the pixel arrangement.

The stress concentration region 4326 may be provided along a directionin which the display panel 4311 is bent. For example, in FIG. 2A, thecut portion may be provided from an upper end to a bottom end of thedisplay panel 4311 along a direction which is parallel to orsubstantially parallel to the supporting portion 4308, so that thedirection in which the display panel 4311 is bent can be controlled (thedisplay panel 4311 can be bent in a direction perpendicular to orsubstantially perpendicular to the supporting portion 4308 as selected)and the occurrence of breaking of the signal line driver circuit 4323provided on the FPC 4324 can be suppressed.

The stress concentration region 4326 can be provided inside or outsidethe supporting portion 4308. For example, the stress concentrationregion 4326 is preferably provided outside the supporting portion 4308(e.g., between the supporting portion 4308 and the display portion 4301)in the case where the supporting portion 4308 is provided so as to beclose to the display panel 4311.

Next, a structure of the display device, which is different from that inFIGS. 2A to 2C is described using FIGS. 3A to 3C. FIG. 3A is a planeview of the display device, FIG. 3B is a cross-sectional view along lineA2-B2 of FIG. 3A, and FIG. 3C is a detailed schematic view of the crosssection.

FIGS. 3A to 3C illustrate the case where an IC where the signal linedriver circuit 4323 is formed is mounted on the display panel 4311 by achip on glass (COG) method. More specifically, the signal line drivercircuit 4323 for controlling the display portion 4301 is provided on theelement substrate 4331 included in the display panel 4311, and thesignal line driver circuit 4323 is electrically connected to the printedboard 4325 through the FPC 4324.

As shown in FIGS. 3A to 3C, in the case where the signal line drivercircuit is provided on the display panel, similarly to the case of FIGS.2A to 2C, the stress concentration region 4326 is preferably providedfor the display panel 4311. In this case, the stress concentrationregion 4326 is provided in a region which is different from (is providedso as to avoid) the region in which the signal line driver circuit 4323is provided. For example, when the stress concentration region 4326 isprovided on the sealing substrate 4332 side, the stress which is appliedto the signal line driver circuit 4323 at the time when the displaypanel 4311 is bent can be reduced and the occurrence of breaking of thesignal line driver circuit 4323 can be suppressed.

Next, a structure of the display device, which is different from thosein FIGS. 2A to 2C and FIGS. 3A to 3C is described using FIGS. 4A to 4C.FIG. 4A is a plane view of the display device, FIG. 4B is across-sectional view along line A3-B3 of FIG. 4A, and FIG. 4C is adetailed schematic view of the cross section.

FIGS. 4A to 4C illustrate the case where an IC in which a circuit suchas a signal line driver circuit is formed is provided on a printedboard, and the printed board and a display panel are connected with anFPC. More specifically, the signal line driver circuit 4323 forcontrolling the display portion 4301 is provided on the printed board4327, and the display panel 4311 and the signal line driver circuit 4323are electrically connected to each other through the FPC 4324.

In FIGS. 4A to 4C, the display panel 4311 can be bent with the FPC 4324,and therefore a stress concentration region is not necessarily providedfor the display panel 4311.

Next, examples of the supporting portion 4308 and a configuration of acircuit which can be provided for the supporting portion 4308 aredescribed using FIG. 5.

FIG. 5 illustrates the case where a display control portion 200including a signal line driver circuit is incorporated in the supportingportion 4308. Such a circuit can be formed using an IC formed using anSOI substrate, a semiconductor substrate such as a silicon substrate, orthe like.

The display control portion 200 can include a CPU 201, a memory portion203, a power feeding portion 205, a power supply circuit 207, an imagesignal generation circuit 215, the signal line driver circuit 4323, anoperation portion 219, and the like. Those components can be connectedto each other through an interface or the like. The display controlportion 200 is electrically connected to the display panel 4311.Although the operation portion 219 is provided in the supporting portion4308 in this case, the operation portion 219 can be provided on thedisplay panel 4311.

The CPU 201 controls the operation of the whole display device.

Data to be displayed on the display portion 4301 is input to a datainput portion 211 from an external device. Note that the data inputportion 211 may include an antenna 216 for transmitting/receiving datato/from an external device. In that case, the data input portion 211 hasa function of transferring data received by the antenna 216 or datastored in a memory medium (an external memory 213) to an internal memory209.

The memory portion 203 can include the internal memory 209, the datainput portion 211, and the external memory 213. Data to be displayed onthe display portion 4301, a program for operating the display device, orthe like can be recorded in the internal memory 209, the data inputportion 211, and the external memory 213.

The internal memory 209 includes a memory portion for storing a programfor processing a signal output to the image signal generation circuit215 and/or the power supply circuit 207 on the basis of a signal fromthe power feeding portion 205, the operation portion 219, or the like,data transferred from the data input portion 211, or the like. Asexamples of the internal memory 209, a DRAM (dynamic random accessmemory), an SRAM (static random access memory), a mask ROM (read onlymemory), a PROM (programmable read only memory), and the like are given.

As an example of the external memory 213, a memory medium such as an ICcard or a memory card is given.

The power feeding portion 205 includes a secondary battery, a capacitor,and the like. A reduction in size of the power feeding portion 205 ispossible when, for example, a lithium battery, preferably, a lithiumpolymer battery utilizing a gel electrolyte, a lithium ion battery, orthe like is used as the secondary battery. Needless to say, any batterycan be used as long as it can be charged, and a battery that can becharged and discharged, such as a nickel-metal hydride battery, anickel-cadmium battery, an organic radical battery, a lead storagebattery, an air secondary battery, a nickel-zinc battery, or asilver-zinc battery may be used. As the capacitor, an electric doublelayer capacitor, a lithium ion capacitor, another capacitor with highcapacitance, or the like can be used. The capacitor is preferably usedbecause it is less likely to be deteriorated even if the number ofcharging and discharging is increased and is excellent in rapidcharging. The shape of the power feeding portion 205 may be sheet-like,cylinder-like, prism-like, plate-like, coin-like, or the like, which canbe selected as appropriate.

Further, the power feeding portion 205 can have a structure in whichelectric power is wirelessly supplied. In that case, an antenna may beprovided for the power feeding portion 205.

The power supply circuit 207 is a circuit for controlling power supplyto a display element in accordance with the control by the CPU 201, inorder to perform display/non-display on the display panel 4311.

The operation portion 219 can be provided with a keyboard, an operationbutton, or the like. In the case where the operation portion 219 isprovided for the display panel 4311, the display portion 4301 canfunction as a touch display, so that the display portion can function asan operation portion.

The structure in which the display control portion 200 is incorporatedin the supporting portion 4308 is illustrated in FIG. 5, and a so-calledpower device such as a switching power source or a DC-DC converter mayfurther be provided.

Further, in the display device illustrated in FIG. 5, by operation ofthe operation portion 219, power input and switching of display can beperformed. The display device may have a structure in which the displayportion 4301 functions as a touch display so as to be operated bytouching with a finger or an input pen.

As described above, by incorporating the display control portion 200 inthe supporting portion 4308, the display control portion 200 can beprotected by a housing. Further, the thickness of the display device canbe reduced.

In Embodiments 1 and 2, the scanning line driver circuits 4321 a and4321 b are provided along the display portion 4301 on the display panel4311; and the present invention is not limited thereto.

For example, as illustrated in FIG. 6A, in the display panel 4311, thescanning line driver circuits 4321 a and 4321 b can be provided so thatthe distance between the scanning line driver circuits 4321 a and 4321 band the supporting portion 4308 is larger than that between the displayportion 4301 and the supporting portion 4308. In general, the density ofelements included in each of the scanning line driver circuits 4321 aand 4321 b is higher than that in the pixel circuit; therefore, theprovision of the scanning line driver circuits 4321 a and 4321 b awayfrom the portion at which the display panel 4311 is bent makes itpossible to suppress the occurrence of breaking of the scanning linedriver circuits 4321 a and 4321 b.

As illustrated in FIGS. 6B and 6C, each of the scanning line drivercircuits 4321 a and 4321 b may be divided into a plurality of circuitportions of scanning line driver circuits, and the plurality of circuitportions of scanning line driver circuits may be provided so as to bespaced from each other; accordingly, even in the case where the displaypanel 4311 is bent, stress applied to the scanning line driver circuits4321 a and 4321 b can be reduced and the occurrence of breaking of thescanning line driver circuits 4321 a and 4321 b can be suppressed. InFIG. 6B, each of the scanning line driver circuits 4321 a and 4321 b isdivided into two circuit portions of scanning line driver circuits. InFIG. 6C, each of the scanning line driver circuits 4321 a and 4321 b isdivided into four circuit portions of scanning line driver circuits. Thenumber of division of each scanning line driver circuit is not limitedthereto.

As illustrated in FIG. 6D, the scanning line driver circuit (either oneof the scanning line driver circuit 4321 a and the scanning line drivercircuit 4321 b) may be provided at one end portion of the display panel4311. This makes it possible to reduce the frame size of the displaydevice.

Embodiment 2 can be implemented in appropriate combination with anystructure described in the other embodiments.

Embodiment 3

In this embodiment, examples of the function effect of the aboveembodiments in the case where a display device including a flexibledisplay panel is bent to be used will be described using FIGS. 7A and7B, 8A to 8C, 9A to 9C, and 10A to 10C.

First, description is made on a front plane view and a top plane view ofthe case where a user uses the display device, illustrated in FIG. 7Aand FIG. 7B respectively.

The display device illustrated in FIG. 7A includes the display panel4311 and the supporting portion 4308. The display panel 4311 includes adisplay portion 4301, and display on the display portion 4301 iscontrolled by the scanning line driver circuit 4321 for supplying ascanning signal to the display portion 4301 and the signal line drivercircuit 4323 for supplying an image signal to the display portion 4301.In FIG. 7A, a user's hand 4350 gripping the supporting portion 4308 isalso illustrated. Further, in the front plane view of FIG. 7A, a line ofsight when the top plane view of FIG. 7B is seen is also illustrated.

In the top plane view shown in FIG. 7B, the display panel 4311 and thesupporting portion 4308 are illustrated. As shown in FIG. 7B, when auser uses the display device with his/her hand 4350, a bending portion(hereinafter referred to as a bending portion C) is formed in a rangeindicated by an arrow C and a non-bending portion (hereinafter referredto as a non-bending portion D) is formed in a range indicated by anarrow D in the flexible display panel.

Note that in FIG. 7B, as an example, description is made on the casewhere the bending portion C of the display panel 4311 is positioned onthe side which is near the supporting portion 4308 and the non-bendingportion D is positioned on the side which is far from the supportingportion 4308. The state of bending is different between the bendingportion C and the non-bending portion D depending on the structure ofthe supporting portion 4308 and a material of a substrate of the displaypanel. Therefore, the bending portion C may be positioned on the sidewhich is far from the supporting portion 4308 and the non-bendingportion D may be positioned on the side which is near the supportingportion 4308.

The display device has a structure in which the display panel 4311 issupported by the supporting portion 4308; therefore, the bending portionC and the non-bending portion D are formed in the display panel 4311 ina direction (indicated by an arrow 7002 in FIG. 7B) which isperpendicular or substantially perpendicular to a direction in which thesupporting portion 4308 extends. Accordingly, the signal line drivercircuit 4323 thus provided does not prevent bending in the directionwhich is perpendicular or substantially perpendicular to the supportingportion 4308 and the occurrence of breaking of the signal line drivercircuit 4323 of can be prevented. Further, the scanning line drivercircuit 4321, which is provided at the edge portion of the display panelin a direction parallel or substantially parallel to the supportingportion 4308, can be manufactured through the same process as theprocess for manufacturing the display portion, which leads to costreduction and reduction of leading of a wiring to the display portion ascompared to the case where the scanning line driver circuit 4321 isprovided for the supporting portion 4308. Note that a plurality ofbending portions C and/or a plurality of non-bending portions D may beprovided, and the bending portion C and the non-bending portion D may beprovided alternately. A stress concentration region may be provided forthe display panel, so that the bending portion C and the non-bendingportion D may be formed artificially.

Next, description is made on the arrangement of the scanning line drivercircuit 4321 with respect to the bending portion C and the non-bendingportion D. FIGS. 8A to 8C are, similarly to FIG. 7A, front plane viewsat the time when the display device is used.

In FIG. 8A, description is made on the case where the bending portion Cis positioned on the side which is near the supporting portion 4308 andthe non-bending portion D is positioned on the side which is far fromthe supporting portion 4308. Therefore, the scanning line driver circuit4321 is provided such that the non-bending portion D is positioned onthe side which is far from the supporting portion 4308. A scanningsignal may be supplied to a pixel TFT 4352 in the display portion byleading of a wiring extended from the scanning line driver circuit 4321,to each scanning line of the display portion. A control signal such as aclock signal for driving the scanning line driver circuit 4321 may besupplied through a wiring extended from an image signal generatingcircuit in the supporting portion 4308. A wiring for electricalconnection between circuits is formed by microfabrication of a metalfilm or the like, and a semiconductor film of a transistor included inthe scanning line driver circuit is formed using a semiconductormaterial such as a silicon film. The ductility of a metal film is higherthan that of a semiconductor material, and the metal film is lessdamaged than the semiconductor material by bending. Therefore, a wiringwhich is connected to the scanning line driver circuit is provided in aportion corresponding to the bending portion C and the transistorincluded in the scanning line driver circuit is provided in a portioncorresponding to the non-bending portion D, whereby damage on thesemiconductor film of the transistor caused by bending can besuppressed. Accordingly, by arranging the scanning line driver circuit4321 as shown in FIG. 8A, occurrence of breaking of a circuit at thetime when a user uses the display device with his/her hand 4350 can besuppressed.

Shown in FIG. 8B is a structure in which the bending portions C and thenon-bending portions D are provided alternately from the side which isnear the supporting portion 4308 to the side which is far from there.Therefore, the scanning line driver circuit 4321 is provided byproviding a driver circuit into a plurality of circuit portions ofdriver circuits and disposing them to be spaced from each other in thenon-bending portions B. A scanning signal may be supplied to the pixelTFT 4352 in the display portion by leading of a wiring extended from thescanning line driver circuit 4321. A control signal such as a clocksignal for driving the scanning line driver circuit 4321 may be suppliedthrough a wiring extended from an image signal generating circuit in thesupporting portion 4308. A signal which is transmitted between pulsesignal generating circuits such as flip flops included in the scanningline driver circuit may be supplied through a wiring. A wiring forelectrical connection between circuits is formed by microfabrication ofa metal film or the like, and a semiconductor film of a transistorincluded in the scanning line driver circuit is formed using asemiconductor material such as a silicon film. The ductility of a metalfilm is higher than that of a semiconductor material, and the metal filmis less damaged than the semiconductor material by bending. Therefore, awiring which is connected to the scanning line driver circuit isprovided in a portion corresponding to the bending portion C and thetransistor included in the scanning line driver circuit is provided in aportion corresponding to the non-bending portion D, whereby damage onthe semiconductor film of the transistor caused by bending can bedecreased. Further, in FIG. 8B, the driver circuit is divided into aplurality of circuit portions of driver circuits and they are providedto be spaced from each other, whereby a stress which is applied to thescanning line driver circuit at the time of bending can be dispersed.Accordingly, by arranging the scanning line driver circuit 4321 as shownin FIG. 8B, occurrence of breaking of a circuit at the time when a useruses the display device with his/her hand 4350 can be suppressed moreeffectively.

In FIG. 8B, the scanning line driver circuits 4321 may be provided foran upper portion and a bottom portion of the display portion of thescanning line driver circuit 4321, as the scanning line driver circuit4321 a and the scanning line driver circuit 4321 b so as to makeredundant or spread the function for outputting a scanning signal. FIG.8C is a view of the display panel in which the scanning line drivercircuits are provided for an upper portion and a bottom portion of thedisplay panel. Scanning signals supplied to the pixel TFTs 4352 aresupplied by the scanning line driver circuit 4321 a and the scanningline driver circuit 4321 b provided for the upper portion and the bottomportion of the display panel, whereby a pulse signal generating circuitsuch as a flip flop included in the scanning line driver circuit can bereduced; accordingly, the occurrence of breaking of a circuit at thetime when a user uses the display device with his/her hand 4350 can besuppressed.

Through the above, illustrating specific examples in FIGS. 8B and 8C, anadvantage of the case where a scanning line driver circuit is notprovided in the region corresponding to the bending portion C butprovided in the region corresponding to the non-bending portion D isdescribed. With these structures, a stress which is applied to thescanning line driver circuit at the time of bending can be dispersed, sothat the occurrence of breaking of a circuit at the time when a useruses the display device with his/her hand 4350 can be suppressed.

Next, examples in which a stress concentration region for artificiallyforming the bending portion C and the non-bending portion D in thedisplay panel in the case where the driver circuit is divided into aplurality of circuit portions of scanning line driver circuits and theyare spaced from each other as illustrated in FIGS. 8B and 8C areillustrated in FIGS. 9A to 9C and FIGS. 10A to 10C. FIG. 9A is a planeview of the display device, FIGS. 9B and 9C are examples of across-sectional view along line E1-F1 of FIG. 9A. FIG. 10A is a planeview of the display device, FIGS. 10B and 10C are examples of across-sectional view along line E2-F2 of FIG. 10A.

In FIG. 9A, the display panel 4311, the supporting portion 4308, thedisplay portion 4301, the scanning line driver circuit 4321, and thesignal line driver circuit 4323 are shown. The scanning line drivercircuit 4321 is divided into two circuit portions of scanning linedriver circuits, and they are spaced from each other with a wiring 920interposed therebetween. It is preferable that a stress concentrationregion 921 be formed to overlap the wiring 920. FIG. 9B is across-sectional view in a direction perpendicular to the supportingportion; as an example, a cut portion 922 a and a cut portion 922 b areprovided for a sealing substrate 923 and an element substrate 924respectively in the stress concentration region 921 which overlaps thewiring 920. As shown in FIG. 9C, a reinforcing plate 925 may be attachedonto the scanning line driver circuit 4321 of the element substrate 924and the sealing substrate 923, so that the cut portion 922 a and the cutportion 922 b are formed. The cut portion 922 a and the cut portion 922b may be provided so as to be parallel to the long-axis direction of thesupporting portion 4308, or may be provided partly.

The stress concentration region means a region where a stress formed bydeformation of a material due to cutting or the like, change of thestrength against bending and/or extension due to attachment of amaterial or the like, or the like is concentrated.

Division of the scanning line driver circuit means a division of aregion where a layout including a circuit element such as a TFT and awiring is repeated, by a region for leading of a wiring.

In FIG. 10A, similarly to FIG. 9A, the display panel 4311, thesupporting portion 4308, the display portion 4301, the scanning linedriver circuit 4321, and the signal line driver circuit 4323 are shown.The signal line driver circuit 4323 is provided by being divided intofour circuit portions of signal line driver circuits and by disposingthem so as to be spaced from each other with the wiring 920 interposedtherebetween. It is preferable that the stress concentration region 921be formed to overlap the plurality of wirings 920. FIG. 10B is across-sectional view in a direction perpendicular to the supportingportion; as an example, a plurality of cut portions 922 a and aplurality of cut portions 922 b are provided for the sealing substrate923 and the element substrate 924 respectively in the stressconcentration regions 921 which overlap the wirings 920. As shown inFIG. 10C, the reinforcing plate 925 may be attached onto the scanningline driver circuit 4321 of the element substrate 924 and the sealingsubstrate 923, so that the plurality of cut portions 922 a and theplurality of cut portions 922 b are formed. The plurality of cutportions 922 a and the plurality of cut portions 922 b may be providedso as to be parallel to the long-axis direction of the supportingportion 4308, or may be provided partly.

The division numbers of the scanning line driver circuits shown in FIGS.9A to 9C and FIGS. 10A to 10C are examples for description; the scanningline driver circuit is divided as appropriate to be provided.

As described above, according to one structure of this embodiment,occurrence of breaking of a scanning line driver circuit at the timewhen a display device is used can be suppressed more effectively.Further, according to one structure of this embodiment, a stressconcentration region is provided for a display panel by a cut portion orthe like in advance, so that occurrence of breaking of a scanning linedriver circuit can be suppressed more effectively.

Embodiment 3 can be implemented in appropriate combination with anystructure described in the other embodiments.

Embodiment 4

In Embodiment 4, an example of a display panel provided for a displaydevice is described. A variety of display panels including any displayelement can be applied, and the display panel may be either apassive-matrix type or an active-matrix type.

As the display panel, an electronic paper, a light-emitting displaypanel (electroluminescence panel), a liquid crystal display panel, orthe like can be used. The display panel is a panel in which a displayelement is sealed, and to which a connector such as a flexible printedcircuit (FPC), tape automated bonding (TAB) tape, or a tape carrierpackage (TCP) is attached and an external circuit including a signalline driver circuit is electrically connected. An IC including a signalline driver circuit may be mounted onto the display panel by chip onglass (COG).

As the display panel 4311, either a dual-display panel in which displayis performed on both sides or a single-sided display panel in whichdisplay is performed on one side may be used. As the dual-display typepanel, a dual-emission type display panel may be used or twoone-side-emission type display panels may be attached to be used. Twoliquid crystal display panels with a backlight (preferably a thin ELpanel) provided therebetween may be used.

Examples of the dual-display type panel which is applicable to thedisplay panel 4311 are illustrated in FIGS. 11A to 11C. Note that inFIGS. 11A to 11C, each arrow indicates a direction in which lightemission is extracted.

FIG. 11A illustrates a display panel 4313 in which a display element 102is provided between a substrate 100 and a substrate 101, and a firstdisplay portion 4302 and a second display portion 4310 are provided onthe substrate 100 side and the substrate 101 side, respectively. Displayis performed on the first display portion 4302 and the second displayportion 4310 by the display element 102; therefore, the substrates 100and 101 have light-transmitting properties. It is preferable that an ELelement that is a self-luminous light-emitting element be used as thedisplay element 102. In the case of using light entering the displaypanel 4313, a liquid crystal display element or an electrophoreticdisplay element can be used as the display element 102.

FIG. 11B illustrates a display panel 4313 in which asingle-sided-display panel in which a display element 114 is providedbetween a substrate 110 and a substrate 112 and a single-sided-displaypanel in which a display element 115 is provided between a substrate 111and a substrate 113 are stacked, and the first display portion 4302 andthe second display portion 4310 are provided on the substrate 100 sideand the substrate 101 side, respectively. Display is performed on thefirst display portion 4302 and the second display portion 4310 by thedisplay element 114 and the display element 115, respectively;therefore, the substrates 110 and 111 have light-transmittingproperties. To the contrary, the substrate 112 and the substrate 113 donot necessarily have light-transmitting properties but may havelight-reflecting properties. The single-sided-display panels may beattached to each other by bonding the substrates 112 and 113 with abonding layer. Either one of the substrate 112 and the substrate 113 maybe provided.

It is preferable that EL elements be used as the display element 114 andthe display element 115. In the case of using light entering the displaypanel 4313, a liquid crystal display element or an electrophoreticdisplay element can be used as each of the display element 114 and thedisplay element 115. In order to enhance the light extractionefficiency, a reflective display panel is preferably used as thesingle-sided-display panel.

A backlight may be provided between light-transmissive liquid crystaldisplay panels, so that the display panel 4313 is formed. FIG. 11Cillustrates a display panel 4313 in which a light-transmissive liquidcrystal display panel in which a display element 124 is provided betweena substrate 120 and a substrate 122 and a light-transmissive liquidcrystal display panel in which a display element 125 is provided betweena substrate 121 and a substrate 123 are stacked with a backlight 126which functions as a light source provided therebetween, and the firstdisplay portion 4302 and the second display portion 4310 are provided onthe substrate 120 side and the substrate 121 side, respectively. Displayis performed on the first display portion 4302 by light from thebacklight 126 and the display element 124 and display is performed onthe second display portion 4310 by light from the backlight 126 and thedisplay element 125; therefore, the substrates 120, 121, 122, and 123have light-transmitting properties.

The attachment of the backlight may be performed by bonding using abonding layer. Either one of the substrate 122 and the substrate 123 maybe provided. It is preferable that a thin EL panel be used as thebacklight 126 because the thickness of the display panel 4313 can bereduced.

In the case of a single-sided-display panel, it is preferable that anon-light-transmissive or reflective housing be provided on the side onwhich a display portion is not provided because the display panel can bereinforced.

Modes of the display panel are described below using FIGS. 12A and 12B,13, 14, and 16. FIGS. 12A and 12B, 13, 14, and 16 correspond tocross-sectional views along line M-N in FIG. 4A. FIGS. 12A and 12B, 13,14, and 16 are examples of the case where the FPC 4324 is attached tothe display panel 4311 including the display portion 4301 including apixel circuit and the scanning line driver circuit 4321 a; the displayportion 4301 and the scanning line driver circuit 4321 a provided overthe element substrate 4331 are sealed with the sealing substrate 4332 bya sealant 4005.

As shown in FIGS. 12A and 12B, and FIGS. 13, 14, and 16, the displaypanel 4311 includes a connection terminal electrode 4015 and a terminalelectrode 4016, and the connection terminal electrode 4015 and theterminal electrode 4016 are electrically connected to a terminalincluded in the FPC 4324 through an anisotropic conductive film 4019.

The connection terminal electrode 4015 is formed using the sameconductive film as a first electrode layer 4030, and the terminalelectrode 4016 is formed using the same conductive film as each of thesource and drain electrode layers included in thin film transistors 4010and 4011.

Further, as shown in FIGS. 4A to 4C, the signal line driver circuit 4323formed using a single crystal semiconductor film or a polycrystalsemiconductor film over a substrate is mounted by an FPC so as to beprovided for the supporting portion 4308. Various signals and potentialsare supplied to the signal line driver circuit 4323, the scanning linedriver circuit 4321 a, and the display portion 4301 from the FPC 4324.

Note that there is no particular limitation on the connection method ofthe signal line driver circuit 4323: a COG method, a wire bondingmethod, a TAB method, or the like can be used.

The display portion 4301 and the scanning line driver circuit 4321 awhich are provided over the element substrate 4331 each include aplurality of thin film transistors; in FIGS. 12A and 12B, and FIGS. 13,14, and 16, the thin film transistor 4010 included in the displayportion 4301 and the thin film transistor 4011 included in the scanningline driver circuit 4321 a are illustrated. Over the thin filmtransistors 4010 and 4011, insulating layers 4020 and 4021 are provided.An insulating film 4023 is an insulating film serving as a base film.

A variety of thin film transistors can be applied to the thin filmtransistors 4010 and 4011 without particular limitation. FIGS. 12A and12B, and FIGS. 13, 14, and 16 each illustrate an example in whichinverted-staggered thin film transistors having a bottom-gate structureare used as the thin film transistors 4010 and 4011. Although the thinfilm transistors 4010 and 4011 are channel-etched thin film transistorsin the drawings, a channel-protective inverted-staggered thin filmtransistor in which a channel protective film is provided over asemiconductor layer may be used.

In the display panel, the thin film transistor 4010 included in thedisplay portion 4301 is electrically connected to a display element. Avariety of display elements can be used as the display element as longas display can be performed.

As a display panel, an electronic paper can be used. As for theelectronic paper, there are many types: an electric field, a magneticfield, light, heat, or the like is used in an image writing method; anda change of a form or a position, a physical change, or the like is usedas for a change of a display medium. For example, a twist ball-type, anelectrophoresis type, a powder system type (also called a tonerdisplay), a liquid crystal type, and the like can be given as examplesthereof.

FIGS. 12A and 12B and FIG. 16 illustrate examples of the case where anactive-matrix electronic paper is used as the display panel 4311.Electronic paper has advantages such as readability which is as high asthat of paper media, low power consumption compared to other displaypanels, and thin light form.

FIGS. 12A and 12B and FIG. 16 illustrate active-matrix electronic papersas examples of the display panel.

The electronic paper in FIG. 12A is an example of a display device usinga twist ball display method. The twist ball display method refers to amethod in which spherical particles each colored in black and white arearranged between electrode layers included in a display element, and apotential difference is generated between the electrode layers tocontrol the orientation of the spherical particles, so that display isperformed.

Between the first electrode layer 4030 connected to the thin filmtransistor 4010 and a second electrode layer 4031 provided for thesealing substrate 4332, spherical particles 4613 each of which includesa black region 4615 a, a white region 4615 b, and a cavity 4612 which isfilled with liquid around the black region 4615 a and the white region4615 b, are provided. A space around the spherical particles 4613 isfilled with a filler 4614 such as a resin. The second electrode layer4031 corresponds to a common electrode (counter electrode). The secondelectrode layer 4031 is electrically connected to a common potentialline.

Instead of the twist ball, an electrophoretic element can be used. Anexample of the case where an electrophoretic element is used as adisplay element is illustrated in FIG. 12B. Microcapsules 4713 eachhaving a diameter of about 10 μm to 200 μm, in which transparent liquid4712, negatively charged black microparticles 4715 a as first particles,and positively charged white microparticles 4715 b as second particlesare encapsulated, are used.

In the microcapsules 4713 provided between the first electrode layer4030 and the second electrode layer 4031, when an electric field isapplied by the first electrode layer 4030 and the second electrode layer4031, the white microparticles 4715 b and the black microparticles 4715a move to opposite directions to each other, so that white or black canbe displayed. A display element using this principle is anelectrophoretic display element. The electrophoretic display element hashigh reflectivity, and thus, an auxiliary light is not needed, powerconsumption is low, and a display portion can be recognized in a dimplace. In addition, even when power is not supplied to the displayportion, an image which has been displayed once can be maintained.Accordingly, a displayed image can be stored even when the display panelis distanced from an electric wave source.

Note that the first particle and the second particle each containpigment and do not move without an electric field. Moreover, the colorsof the first particle and the second particle are different from eachother (the color of either one of them may be colorless).

A solution in which the above microcapsules are dispersed in a solventis referred to as electronic ink. This electronic ink can be printed ona surface of glass, plastic, cloth, paper, or the like. Furthermore, byusing a color filter or particles that have a pigment, color display canbe performed.

Note that the first particles and the second particles in themicrocapsules may be formed using a single material selected from aconductive material, an insulating material, a semiconductor material, amagnetic material, a liquid crystal material, a ferroelectric material,an electroluminescent material, an electrochromic material, and amagnetophoretic material, or a composite material of any of these.

Electronic Liquid Powder (registered trademark) can be used for anelectronic paper using liquid powders. An example of the case where anelectronic liquid powder is used as the display element is illustratedin FIG. 16. Positively charged black liquid powders 4815 a andnegatively charged white liquid powders 4815 b are contained in a space4812 segmented by the first electrode layer 4030, the second electrodelayer 4031, and a rib 4814. The space 4812 is filled with air.

When an electric field is applied by the first electrode layer 4030 andthe second electrode layer 4031, the black liquid powders 4815 a and thewhite liquid powders 4815 b move in opposite directions to each other,so that white or black can be displayed. As the liquid powders, colorpowders of red, yellow, and/or blue may be used.

A light-emitting element using electroluminescence (an EL element) maybe used as the display element. Light-emitting elements usingelectroluminescence are classified according to whether a light-emittingmaterial is an organic compound or an inorganic compound; in general,the former is called an organic EL element, and the latter is called aninorganic EL element.

In an organic EL element, voltage is applied to a light-emittingelement, so that electrons and holes are injected from a pair ofelectrodes into a layer containing a light-emitting organic compound,whereby current flows. The carriers (electrons and holes) arerecombined, and thus, the light-emitting organic compound is excited.The light-emitting organic compound returns to a ground state from theexcited state, thereby emitting light. Owing to such a mechanism, thislight-emitting element is called a current-excitation light-emittingelement.

Inorganic EL elements are classified according to their elementstructures into a dispersion-type inorganic EL element and a thin-filminorganic EL element. A dispersion-type inorganic EL element includes alight-emitting layer in which particles of a light-emitting material aredispersed in a binder, and its light emission mechanism isdonor-acceptor recombination type light emission that uses a donor leveland an acceptor level. A thin-film inorganic EL element has a structurewhere a light-emitting layer is sandwiched between dielectric layers,which are further sandwiched between electrodes, and its light emissionmechanism is localized type light emission that uses inner-shellelectron transition of metal ions. Description is made here using anorganic EL element as a light-emitting element.

In order to extract light emitted from the light-emitting element, atleast one of the pair of electrodes is transparent. A thin filmtransistor and a light-emitting element are formed over a substrate. Anyof light-emitting elements having the following structures can beapplied: a top emission structure in which light emission is extractedthrough the surface opposite to the substrate; a bottom emissionstructure in which light emission is extracted through the surface onthe substrate side; a dual emission structure in which light emission isextracted through the surface opposite to the substrate and the surfaceon the substrate side; and the like.

An example of the case where a light-emitting display panel (EL panel)is used as the display panel 4311 is illustrated in FIG. 13. Alight-emitting element 4513 which is a display element is electricallyconnected to the thin film transistor 4010 provided in the displayportion 4301. A structure of the light-emitting element 4513 is notlimited to the stacked-layer structure shown in FIG. 13, including thefirst electrode layer 4030, an electroluminescent layer 4511, and thesecond electrode layer 4031. The structure of the light-emitting element4513 can be changed as appropriate depending on a direction in whichlight is extracted from the light-emitting element 4513, or the like.

A partition wall 4510 is formed using an organic resin film, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition wall 4510 be formed using a photosensitivematerial to have an opening portion over the first electrode layer 4030so that a sidewall of the opening portion is formed as a tilted surfacewith continuous curvature.

The electroluminescent layer 4511 may be formed using a single layer ora plurality of layers stacked.

A protective film may be formed over the second electrode layer 4031 andthe partition wall 4510 in order to prevent entry of oxygen, hydrogen,moisture, carbon dioxide, or the like into the light-emitting element4513. As the protective film, a silicon nitride film, a silicon nitrideoxide film, a DLC film, or the like can be formed. A filler 4514 isprovided in a space sealed with the element substrate 4331, the sealingsubstrate 4332, and the sealant 4005 so as to seal closely. It ispreferable that a panel be packaged (sealed) with a protective film(such as a laminate film or an ultraviolet curable resin film) or acover material with high air-tightness and little degasification so thatthe panel is not exposed to the outside air, in this manner.

As the filler 4514, an ultraviolet curable resin or a thermosettingresin can be used as well as an inert gas such as nitrogen or argon. Forexample, PVC (polyvinyl chloride), acrylic, polyimide, an epoxy resin, asilicone resin, PVB (polyvinyl butyral), or EVA (ethylene vinyl acetate)can be used. For example, nitrogen is used for the filler.

In addition, if needed, an optical film such as a polarizing plate, acircularly polarizing plate (including an elliptically polarizingplate), a retardation plate (a quarter-wave plate or a half-wave plate),or a color filter may be provided as appropriate on a light-emittingsurface of the light-emitting element. Further, the polarizing plate orthe circularly polarizing plate may be provided with an anti-reflectionfilm. For example, anti-glare treatment by which reflected light isdiffused by roughness on the surface so as to reduce the glare can beperformed.

An example of the case where a liquid crystal display panel is used asthe display panel 4311 is illustrated in FIG. 14. In FIG. 14, a liquidcrystal element 4013 which is a display element includes the firstelectrode layer 4030, the second electrode layer 4031, and a liquidcrystal layer 4008. Insulating films 4032 and 4033 serving asorientation films are provided to hold the liquid crystal layer 4008therebetween. The second electrode layer 4031 is provided on the sealingsubstrate 4332 side, and the first electrode layer 4030 and the secondelectrode layer 4031 are stacked with the liquid crystal layer 4008provided therebetween.

Reference numeral 4035 indicates a columnar spacer formed by selectivelyetching the insulating film, and the columnar spacer 4035 is provided inorder to control the thickness of the liquid crystal layer 4008 (a cellgap). A spherical spacer may be used as well.

Although not shown in the liquid crystal display device in FIG. 14, acolor filter (a coloring layer), a black matrix (a light-shieldinglayer), an optical member (an optical substrate) such as a polarizingmember, a retardation member, or an anti-reflection member, and the likeare provided as appropriate. For example, circular polarization by usinga polarizing substrate and a retardation substrate may be used. Abacklight, a side light, or the like may be used as a light source; asthe backlight, it is preferable to use an EL panel in the point of smallthickness.

Liquid crystal exhibiting a blue phase for which an alignment film isnot needed may be used. A blue phase is one of liquid crystal phases,which is generated before a cholesteric phase changes into an isotropicphase while temperature of cholesteric liquid crystal is increased.Since the blue phase is generated within a narrow range of temperature,liquid crystal composition containing a chiral agent at 5 wt % or moreso as to improve the temperature range is used for the liquid crystallayer 4008. The liquid crystal composition which includes liquid crystalexhibiting a blue phase and a chiral agent has a response time as shortas 10 μs to 100 μs. Further, the liquid crystal composition has opticalisotropy. Therefore, an alignment treatment is not needed and thedependency on the viewing angle is less.

Although FIG. 14 illustrates the example of a light-transmissive liquidcrystal display panel, the present invention can also be applied to areflective liquid crystal display panel or a light-semi-transmissiveliquid crystal display panel.

In FIGS. 12A and 12B, and FIGS. 13, 14, and 16, a plastic havinglight-transmitting properties can be used as each of the elementsubstrate 4331 and the sealing substrate 4332. As the plastic, afiberglass-reinforced plastics (FRP) plate, a polyvinyl fluoride (PVF)film, a polyester film, or an acrylic resin film can be used. A sheetwith a structure in which an aluminum foil is sandwiched between PVFfilms or polyester films can be used.

The insulating layer 4020 serves as a protective film of a thin filmtransistor.

The protective film is provided to prevent entry of contaminantimpurities such as organic substance, metal, or moisture existing in theair and is preferably a dense film. The protective film may be formedusing a single layer of a silicon oxide film, a silicon nitride film, asilicon oxynitride film, a silicon nitride oxide film, an aluminum oxidefilm, an aluminum nitride film, an aluminum oxynitride film, or analuminum nitride oxide film, or a stacked layer thereof by a sputteringmethod.

The insulating layer 4021 serving as a planarizing insulating film canbe formed using an organic material having heat resistance, such asacrylic, polyimide, benzocyclobutene, polyamide, or epoxy. Other thansuch organic materials, it is also possible to use a low-dielectricconstant material (a low-k material), a siloxane-based resin,phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), or thelike. The insulating layer may be formed by stacking a plurality ofinsulating films using any of these materials.

There is no particular limitation on the method for forming theinsulating layers 4020 and 4021: depending on a material thereof,sputtering, an SOG method, spin coating, dipping, spray coating, adroplet discharging method (e.g., an ink-jet method, screen printing, oroffset printing), a doctor knife, a roll coater, a curtain coater, aknife coater, or the like can be used. In the case where the insulatinglayer is formed using a material solution, the semiconductor layer maybe annealed (at 200° C. to 400° C.) at the same time as a baking step;when the step of baking the insulating layer and the annealing of thesemiconductor layer are performed at the same time, the display panelcan be efficiently manufactured.

The display panel displays an image by light transmitted from a lightsource or a display element. Therefore, the substrates and the thinfilms such as insulating films and conductive films provided for thedisplay portion where light is transmitted have light-transmittingproperties with respect to light in the visible-light wavelength range.

The first electrode layer 4030 and the second electrode layer 4031 (eachof which may be called a pixel electrode layer, a common electrodelayer, a counter electrode layer, or the like) for applying voltage tothe display element may have light-transmitting properties orlight-reflecting properties, which depends on the direction in whichlight is extracted, the position where the electrode layer is provided,the pattern structure of the electrode layer, and the like.

The first electrode layer 4030 and the second electrode layer 4031 eachcan be formed using a light-transmitting conductive material such asindium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, indium tin oxide (hereinafter referred to asITO), indium zinc oxide, or indium tin oxide to which silicon oxide isadded.

The first electrode layer 4030 and the second electrode layer 4031 eachcan be formed using one kind or plural kinds selected from metal such astungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium(V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel(Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), orsilver (Ag); an alloy thereof; and a nitride thereof.

A conductive composition containing a conductive high molecule (alsocalled a conductive polymer) can be included in the first electrodelayer 4030 and the second electrode layer 4031. As the conductive highmolecule, a so-called π-electron conjugated conductive polymer can beused. For example, polyaniline or a derivative thereof, polypyrrole or aderivative thereof, polythiophene or a derivative thereof, a copolymerof two or more kinds of them, and the like can be used.

Since a thin film transistor is easily broken by static electricity orthe like, a protection circuit for protecting a driver circuit ispreferably provided. It is preferable that the protection circuitinclude a nonlinear element.

Embodiment 4 can be implemented in appropriate combination with anystructure described in the other embodiments.

Embodiment 5

In Embodiment 5, examples of a material used for forming a displaydevice and an element structure will be described in detail.

A signal line driver circuit is provided in a supporting portion, andtherefore is not necessarily flexible. Accordingly, it is preferablethat a semiconductor integrated circuit chip (IC) which is capable ofhigh-speed operation and in which a semiconductor substrate (asemiconductor wafer) is used be used as the signal line driver circuit.As the semiconductor substrate, a single crystal semiconductor substrateor a polycrystalline semiconductor substrate can be used: for example, asemiconductor wafer such as a silicon wafer or a germanium wafer or acompound semiconductor wafer of gallium arsenide, indium phosphide, orthe like is used.

Alternatively, a substrate (an SOI substrate) having an SOI structure inwhich a single crystal semiconductor layer is provided on an insulatingsurface may be used for the signal line driver circuit. The SOIsubstrate can be formed by a separation by implanted oxygen (SIMOX)method or a Smart-Cut (registered trademark) method. In the SIMOXmethod, oxygen ions are implanted into a single crystal siliconsubstrate to form a layer containing oxygen at a predetermined depth andheat treatment is performed, so that an embedded insulating layer isformed at a predetermined depth from the surface of the single crystalsilicon substrate, whereby a single crystal silicon layer is formed onthe embedded insulating layer. In the Smart-Cut (registered trademark)method, hydrogen ions are implanted into an oxidized single crystalsilicon substrate to form a layer containing hydrogen at a predetermineddepth, the oxidized single crystal silicon substrate is attached toanother semiconductor substrate (such as a single crystalline siliconsubstrate having a silicon oxide film for attachment on its surface),and heat treatment is performed to separate the single crystal siliconsubstrate at the layer containing hydrogen, so that a stacked layer ofthe silicon oxide film and the single crystalline silicon layer isformed on the semiconductor substrate.

As a semiconductor element provided in a circuit portion of the displaydevice, not only a field-effect transistor but also a memory elementwhich uses a semiconductor layer can be employed; accordingly, asemiconductor integrated circuit having functions required for variousapplications can be provided.

There is no particular limitation on the methods by which the scanningline driver circuit and the display portion are provided as long as thescanning line driver circuit and the display portion are provided over aflexible substrate of the display panel. The scanning line drivercircuit and the display portion may be formed directly on the flexiblesubstrate. Alternatively, the scanning line driver circuit and thedisplay portion may be formed on a formation substrate, and then only anelement layer is transferred from the formation substrate to theflexible substrate by a separation method. For example, the scanningline driver circuit and the display portion can be formed on theformation substrate through the same process and transferred to theflexible substrate of the display panel. In that case, since thescanning line driver circuit and the display portion are formed throughthe same process, they are preferably formed using transistors havingthe same structure and material in the point of cost reduction.Therefore, channel layers of transistors included in the scanning linedriver circuit and the display portion are formed using the samematerial.

Alternatively, transferring from a formation substrate to a flexiblesupporting substrate may be performed, and then the whole flexiblesupporting substrate may be attached to a substrate of the displaypanel. For example, a plurality of scanning line driver circuits may beformed over the formation substrate and transferred to the flexiblesupporting substrate, and then the plurality of scanning line drivercircuits are separated individually with the flexible supportingsubstrate divided, and the scanning line driver circuit provided overthe flexible supporting substrate may be attached as many as needed toone display panel. In that case, since the scanning line driver circuitand the display portion are formed through different processes,transistors having different structures and materials can be used.

The above transfer method and direct formation method may be combined.For example, a wiring for electrically connecting a display portion, ascanning line driver circuit, an FPC, and the like may be directlyformed on a flexible substrate of the display panel by a printing methodor the like.

The formation substrate may be selected as appropriate depending on theformation process of the element layer. For example, a glass substrate,a quartz substrate, a sapphire substrate, a ceramic substrate, or ametal substrate having an insulating layer on its surface can be used asthe formation substrate. A plastic substrate having heat resistance tothe processing temperature may be used as well.

As the flexible substrate, an aramid resin, a polyethylene naphthalate(PEN) resin, a polyether sulfone (PES) resin, a polyphenylene sulfide(PPS) resin, a polyimide (PI) resin, or the like can be used. A prepregthat is a structure body in which fiber is impregnated with an organicresin may be used as well.

There is no particular limitation on the method of transferring theelement layer from the formation substrate to another substrate; avariety of methods can be used. For example, a separation layer may beformed between the formation substrate and the element layer.

In this specification, the element layer includes in its category, notonly a semiconductor element layer provided on the element substrateside but also a counter electrode layer or the like provided on thecounter substrate side. Accordingly, the separation step can be used forboth the element substrate side and the sealing substrate side. Further,in view of the simplicity of the manufacturing process, the elementlayer is transferred from the formation substrate to the flexiblesubstrate, and then the manufacturing process can proceed with theflexible substrate temporally attached to a glass substrate or the like.

The separation layer is formed to have a single-layer structure or astacked-layer structure including a layer formed using an element suchas tungsten (W), molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium(Nb), nickel (Ni), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium(Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), orsilicon (Si); or an alloy material or a compound material containing anyof the elements as its main component by a sputtering method, a plasmaCVD method, a coating method, a printing method, or the like. Acrystalline structure of a layer containing silicon may be any one of anamorphous structure, a microcrystalline structure, and a polycrystallinestructure. The coating method includes a spin-coating method, a dropletdischarge method, and a dispensing method in its category here.

In the case where the separation layer has a single-layer structure, itis preferable to form a tungsten layer, a molybdenum layer, or a layercontaining a mixture of tungsten and molybdenum. Alternatively, a layercontaining oxide or oxynitride of tungsten, a layer containing oxide oroxynitride of molybdenum, or a layer containing oxide or oxynitride of amixture of tungsten and molybdenum may be formed. Note that the mixtureof tungsten and molybdenum, for example, corresponds to an alloy oftungsten and molybdenum.

In the case where the separation layer has a stacked-layer structure, itis preferable to form, as a first layer, a tungsten layer, a molybdenumlayer, or a layer containing a mixture of tungsten and molybdenum, andform, as a second layer, oxide, nitride, oxynitride, or nitride oxide oftungsten, molybdenum, or a mixture of tungsten and molybdenum.

In the case where the separation layer is formed to have a stacked-layerstructure including a layer containing tungsten and a layer containingoxide of tungsten, the layer containing tungsten may be formed first andan insulating layer formed of oxide is formed thereover to form a layercontaining oxide of tungsten at the interface between the tungsten layerand the insulating layer. Furthermore, the surface of the layercontaining tungsten may be subjected to thermal oxidation treatment,oxygen plasma treatment, or treatment using a strong oxidizing solutionsuch as ozone water to form a layer containing oxide of tungsten. Plasmatreatment or heat treatment may be performed in an atmosphere of oxygen,nitrogen, or dinitrogen monoxide alone, or a mixed gas of the above gasand another gas. The same applies to the case of forming a layercontaining nitride, oxynitride, or nitride oxide of tungsten: after thelayer containing tungsten is formed, a silicon nitride layer, a siliconoxynitride layer, or a silicon nitride oxide layer may be formedthereover.

Note that for the step of transferring the element layer to anothersubstrate, any of the following methods can be used as appropriate: amethod in which a separation layer is formed between a substrate and anelement layer, a metal oxide film is provided between the separationlayer and the element layer, and the metal oxide film is embrittled bycrystallization, thereby separating the element layer; a method in whichan amorphous silicon film containing hydrogen is provided between asubstrate having high heat resistance and an element layer, and theamorphous silicon film is removed by laser light irradiation or etching,thereby separating the element layer; a method in which a separationlayer is formed between a substrate and an element layer, a metal oxidefilm is provided between the separation layer and the element layer, themetal oxide film is embrittled by crystallization, part of theseparation layer is removed by etching using a solution or a fluoridehalogen gas such as NF₃, BrF₃, or ClF₃, and then the element layer isseparated at the embrittled metal oxide film; a method in which asubstrate over which an element layer is formed is mechanically removedor is removed by etching using a solution or a fluoride halogen gas suchas NF₃, BrF₃, or ClF₃; and the like. Alternatively, a method may be usedin which a film containing nitrogen, oxygen, hydrogen, or the like(e.g., an amorphous silicon film containing hydrogen, an alloy filmcontaining hydrogen, or an alloy film containing oxygen) is used as aseparation layer, and the separation layer is irradiated with laserlight to release nitrogen, oxygen, or hydrogen contained in theseparation layer as a gas, thereby promoting separation between theelement layer and the substrate.

Combination of the above separation methods makes it easier to performthe transferring step. In other words, separation can also be performedwith physical force (e.g., by a machine or the like) after making iteasier for the separation layer and the element layer to be separated bylaser irradiation, etching of the separation layer with a gas or asolution, or mechanical removal of the separation layer with a sharpknife, scalpel, or the like.

The interface between the separation layer and the element layer may bepermeated with a liquid, so that the element layer is separated from thesubstrate. Water or the like can be used as the liquid.

There is no particular limitation on the kind of thin film transistorsincluded in the display device of the present invention. Accordingly, avariety of structures and semiconductor materials can be used for thetransistors.

Examples of the structure of a thin film transistor is described usingFIGS. 15A to 15D. FIGS. 15A to 15D illustrates examples of the thin filmtransistor which can be applied to the thin film transistor 4010 inEmbodiment 5.

In FIGS. 15A to 15D, the insulating film 4023 is formed over the elementsubstrate 4331, and thin film transistors 4010 a, 4010 b, 4010 c, and4010 d are provided over the insulating film 4023. The insulating layers4020 and 4021 are formed over each of the thin film transistors 4010 a,4010 b, 4010 c, and 4010 d, and the first electrode layer 4030 isprovided to be electrically connected to the thin film transistors 4010a, 4010 b, 4010 c, and 4010 d.

The thin film transistor 4010 a has a structure in which wiring layers405 a and 405 b serving as a source and drain electrode layers are incontact with a semiconductor layer 403 without an n⁺ layer interposedtherebetween in the thin film transistor 4010 illustrated in FIGS. 12Aand 12B.

The thin film transistor 4010 a is an inverted-staggered thin filmtransistor in which a gate electrode layer 401, a gate insulating layer402, the semiconductor layer 403, and the wiring layers 405 a and 405 bserving as a source and drain electrode layers are provided over theelement substrate 4331 having an insulating surface and the insulatingfilm 4023.

The thin film transistor 4010 b is a bottom-gate thin film transistor inwhich the gate electrode layer 401, the gate insulating layer 402, thewiring layers 405 a and 405 b serving as a source and drain electrodelayers, n⁺ layers 404 a and 404 b serving as a source and drain regions,and the semiconductor layer 403 are provided over the element substrate4331 having an insulating surface and the insulating film 4023. The n⁺layers 404 a and 404 b are semiconductor layers having lower resistancethan the semiconductor layer 403. In addition, the insulating layer 4020is provided in contact with the semiconductor layer 403 so as to coverthe thin film transistor 4010 b.

The n⁺ layers 404 a and 404 b may be provided between the gateinsulating layer 402 and the wiring layers 405 a and 405 b. The n⁺layers may be provided both between the gate insulating layer and thewiring layers and between the wiring layers and the semiconductor layer.

In the thin film transistor 4010 b, the gate insulating layer 402 existsin the entire region including the thin film transistor 4010 b, and thegate electrode layer 401 is provided between the gate insulating layer402 and the element substrate 4331 having an insulating surface. Thewiring layers 405 a and 405 b and the n⁺ layers 404 a and 404 b areprovided over the gate insulating layer 402. In addition, thesemiconductor layer 403 is provided over the gate insulating layer 402,the wiring layers 405 a and 405 b, and the n⁺ layers 404 a and 404 b.Although not shown, a wiring layer is provided over the gate insulatinglayer 402 in addition to the wiring layers 405 a and 405 b, and thewiring layer extends beyond the perimeter of the semiconductor layer403.

The thin film transistor 4010 c has a structure in which the source anddrain electrode layers are in contact with the semiconductor layerwithout an n⁺ layer interposed therebetween in the thin film transistor4010 b.

In the thin film transistor 4010 c, the gate insulating layer 402 existsin the entire region including the thin film transistor 4010 c, and thegate electrode layer 401 is provided between the gate insulating layer402 and the element substrate 4331 having an insulating surface. Thewiring layers 405 a and 405 b are provided over the gate insulatinglayer 402. In addition, the semiconductor layer 403 is provided over thegate insulating layer 402 and the wiring layers 405 a and 405 b.Although not shown, a wiring layer is provided over the gate insulatinglayer 402 in addition to the wiring layers 405 a and 405 b, and thewiring layer extends beyond the perimeter of the semiconductor layer403.

The thin film transistor 4010 d is a top-gate thin film transistor andan example of a planar thin film transistor. The semiconductor layer 403including the n⁺ layers 404 a and 404 b serving as a source and drainregions is formed over the element substrate 4331 having an insulatingsurface and the insulating film 4023. The gate insulating layer 402 isformed over the semiconductor layer 403, and the gate electrode layer401 is formed over the gate insulating layer 402. In addition, thewiring layers 405 a and 405 b serving as a source and drain electrodelayers are formed in contact with the n⁺ layers 404 a and 404 b. The n⁺layers 404 a and 404 b are semiconductor layers having lower resistancethan the semiconductor layer 403.

A top-gate forward-staggered thin film transistor may be used as thethin film transistor.

Although a single-gate structure is described in this embodiment, amulti-gate structure such as a double-gate structure may be used. Inthat case, a gate electrode layer may be provided above and below thesemiconductor layer, or a plurality of gate electrode layers may beprovided on one side of (above or below) the semiconductor layer.

There is no particular limitation on the semiconductor material used forthe semiconductor layer. Examples of a material used for thesemiconductor layer of the thin film transistor are described below.

As a material used for forming the semiconductor layer included in thesemiconductor element, any of the following can be used: an amorphoussemiconductor (hereinafter, also referred to as “AS”) that is formed bya sputtering method or a vapor-phase growth method using a semiconductormaterial gas typified by silane or germane; a polycrystallinesemiconductor that is obtained by crystallizing the amorphoussemiconductor by utilizing light energy or thermal energy; amicrocrystalline semiconductor (also referred to as a semi-amorphous ormicrocrystal semiconductor, and hereinafter, also referred to as “SAS”);and the like. The semiconductor layer can be deposited by a sputteringmethod, an LPCVD method, a plasma CVD method, or the like.

Considering Gibbs free energy, the microcrystalline semiconductor filmis in a metastable state between an amorphous state and a single crystalstate. In other words, the microcrystalline semiconductor is in a thirdstate that is stable in free energy and has short-range order andlattice distortion. Columnar-like or needle-like crystals grow in thenormal direction to the surface of the substrate. The Raman spectrum ofmicrocrystalline silicon, which is a typical example of amicrocrystalline semiconductor, is located in lower wave numbers than520 cm⁻¹ that represents the peak of the Raman spectrum of singlecrystal silicon. In other words, the peak of the Raman spectrum of themicrocrystalline silicon exists between 520 cm⁻¹ that represents that ofsingle crystal silicon and 480 cm⁻¹ that represents that of amorphoussilicon. In addition, the microcrystalline silicon contains hydrogen orhalogen of at least 1 atomic % or more in order to terminate a danglingbond. Moreover, the microcrystalline silicon contains a rare gas elementsuch as helium, argon, krypton, or neon to further promote latticedistortion, whereby a favorable microcrystalline semiconductor film withimproved stability can be obtained.

This microcrystalline semiconductor film can be formed by ahigh-frequency plasma CVD method with a frequency of several tens ofmegahertz to several hundreds of megahertz, or a microwave plasma CVDapparatus with a frequency of 1 GHz or more. Typically, themicrocrystalline semiconductor film can be formed with silicon hydridesuch as SiH₄, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, or SiF₄ and hydrogen whichis added for dilution. Alternatively, the microcrystalline semiconductorfilm can be formed with, in addition to silicon hydride and hydrogen,one or more kinds of rare gas elements selected from helium, argon,krypton, and neon which is added for dilution. In such a case, the flowrate ratio of hydrogen to silicon hydride is set to 5:1 to 200:1,preferably 50:1 to 150:1, and more preferably 100:1

Hydrogenated amorphous silicon is given as a typical example of anamorphous semiconductor, and polysilicon and the like are given astypical examples of a crystalline semiconductor. Polysilicon(polycrystalline silicon) includes so-called high-temperaturepolysilicon that contains, as its main component, polysilicon formed ata process temperature of 800° C. or higher, so-called low-temperaturepolysilicon that contains, as its main component, polysilicon formed ata process temperature of 600° C. or lower, and polysilicon formed bycrystallizing amorphous silicon by using an element which promotescrystallization, or the like. As described above, a microcrystallinesemiconductor or a semiconductor partially including a crystalline phasecan be used as well.

As the semiconductor material, a compound semiconductor such as GaAs,InP, SiC, ZnSe, GaN, or SiGe can be used as well as silicon (Si) orgermanium (Ge) alone.

In the case of using a crystalline semiconductor film as thesemiconductor layer, the crystalline semiconductor film may be formed byany of a variety of methods (e.g., laser crystallization, thermalcrystallization, or thermal crystallization using an element such asnickel which promotes crystallization). A microcrystalline semiconductorthat is SAS may be crystallized by laser irradiation, so thatcrystallinity thereof can be enhanced. In the case where an elementwhich promotes crystallization is not added, an amorphous silicon filmis heated at 500° C. for one hour in a nitrogen atmosphere before beingirradiated with laser light, whereby hydrogen contained in the amorphoussilicon film is released to a concentration of 1×10²⁰ atoms/cm³ or less.This is because, if the amorphous silicon film contains a large amountof hydrogen, the amorphous silicon film would be destroyed by laserlight irradiation.

There is no particular limitation on the method of adding a metalelement into the amorphous semiconductor film as long as the metalelement can exist in the surface of or inside the amorphoussemiconductor film. For example, a sputtering method, a CVD method, aplasma treatment method (e.g., a plasma CVD method), an adsorptionmethod, or a method of applying a metal salt solution can be used. Amongthese, the method using a solution is useful in terms of easy adjustmentof the concentration of the metal element. At this time, an oxide filmis preferably deposited by UV light irradiation in an oxygen atmosphere,thermal oxidation, treatment with ozone water or hydrogen peroxideincluding a hydroxyl radical, or the like in order to improve thewettability of the surface of the amorphous semiconductor film and tospread an aqueous solution on the entire surface of the amorphoussemiconductor film.

In a crystallization step for crystallizing the amorphous semiconductorfilm to form a crystalline semiconductor film, an element which promotescrystallization (also referred to as a catalytic element or a metalelement) may be added to the amorphous semiconductor film, andcrystallization may be performed by heat treatment (at 550° C. to 750°C. for 3 minutes to 24 hours). As the element which promotes(accelerates) the crystallization, one or more kinds of elementsselected from iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru),rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt),copper (Cu), and gold (Au) can be used.

In order to remove or reduce the element which promotes crystallizationfrom the crystalline semiconductor film, a semiconductor film containingan impurity element is formed in contact with the crystallinesemiconductor film so as to function as a gettering sink. As theimpurity element, an impurity element imparting n-type conductivity, animpurity element imparting p-type conductivity, a rare gas element, orthe like can be used. For example, it is possible to use one or morekinds of elements selected from phosphorus (P), nitrogen (N), arsenic(As), antimony (Sb), bismuth (Bi), boron (B), helium (He), neon (Ne),argon (Ar), krypton (Kr), and xenon (Xe). A semiconductor filmcontaining a rare gas element is formed in contact with the crystallinesemiconductor film containing the element which promotescrystallization, and then heat treatment is performed (at 550° C. to750° C. for 3 minutes to 24 hours). The element promotingcrystallization that is contained in the crystalline semiconductor filmmoves into the semiconductor film containing a rare gas element, andthus the element promoting crystallization which is contained in thecrystalline semiconductor film is removed or reduced. After that, thesemiconductor film containing a rare gas element which functions as agettering sink is removed.

The amorphous semiconductor film may be crystallized by a combination ofthermal treatment and laser light irradiation. Either one of thermaltreatment and laser light irradiation may be performed plural times.

A crystalline semiconductor film may be formed directly over thesubstrate by a plasma method. A crystalline semiconductor film may beselectively formed over the substrate by a plasma method.

An oxide semiconductor may be used for the semiconductor layer. Forexample, zinc oxide (ZnO), tin oxide (SnO₂), or the like can be used. Inthe case of using ZnO for the semiconductor layer, Y₂O₃, Al₂O₃, or TiO₂,a stacked layer thereof, or the like can be used for a gate insulatinglayer, and ITO, Au, Ti, or the like can be used for a gate electrodelayer, a source electrode layer, and/or a drain electrode layer. Inaddition, In, Ga, or the like may be added to Zn—O.

As the oxide semiconductor, a thin film represented by InMO₃ (ZnO)_(m)(m>0) can be used. Here, M denotes one or more of metal elementsselected from gallium (Ga), iron (Fe), nickel (Ni), manganese (Mn), andcobalt (Co). For example, M is gallium (Ga) in some cases, and in othercases, M contains other metal elements in addition to Ga, such as Ga andNi or Ga and Fe. Furthermore, the above oxide semiconductor may containa transition metal element such as Fe or Ni or an oxide of thetransition metal as an impurity element in addition to a metal elementcontained as M. For example, an In—Ga—Zn—O-based non-single-crystal filmcan be used as the oxide semiconductor layer.

As the oxide semiconductor layer (the InMO₃(ZnO)_(m) (m>0) film), anInMO₃(ZnO)_(m) film (m>0) in which M is another metal element may beused instead of the In—Ga—Zn—O-based non-single-crystal film. As theoxide semiconductor which is applied to the oxide semiconductor layer,any of the following oxide semiconductors can be applied as well as theabove: an In—Sn—Zn—O based oxide semiconductor; an In—Al—Zn—O basedoxide semiconductor; a Sn—Ga—Zn—O based oxide semiconductor; anAl—Ga—Zn—O based oxide semiconductor; a Sn—Al—Zn—O based oxidesemiconductor; an In—Zn—O based oxide semiconductor; a Sn—Zn—O basedoxide semiconductor; an Al—Zn—O based oxide semiconductor; an In—O basedoxide semiconductor; a Sn—O based oxide semiconductor; and a Zn—O basedoxide semiconductor.

Embodiment 5 can be implemented in appropriate combination with anystructures described in the other embodiments.

This application is based on Japanese Patent Application serial no.2009-112378 filed with Japan Patent Office on May 2, 2009, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. (canceled)
 2. A display device comprising: adisplay panel comprising: a first plate and a second plate; a firstsubstrate over the first plate and the second plate, the first substratehaving flexibility; a display portion over the first substrate, thedisplay portion comprising: a transistor; and a display elementelectrically connected to the transistor; a first driver circuit overthe first substrate and overlapping with the first plate; and a secondsubstrate over the display portion and the first driver circuit, thesecond substrate having flexibility; and a flexible printed circuit(FPC) attached to an end portion of the display panel, wherein the endportion of the display panel is along a first direction, wherein thedisplay portion is bendable between the first plate and the secondplate, wherein the display portion is bendable along the firstdirection, wherein the first driver circuit is provided along a seconddirection perpendicular to the first direction, and wherein the firstplate and the second plate are attached to the same surface of the firstsubstrate.
 3. The display device according to claim 2, comprising asupporting portion at the end portion of the display panel, wherein theFPC is provided in the supporting portion.
 4. The display deviceaccording to claim 2, wherein the display element is a light-emittingelement.
 5. The display device according to claim 2, wherein the displayelement is a liquid crystal element.
 6. The display device according toclaim 2, wherein the display element is an electrophoretic displayelement.
 7. The display device according to claim 2, wherein the firstplate and the second plate are reinforcing plates.
 8. The display deviceaccording to claim 2, comprising: a third plate over the secondsubstrate and overlapping with the first plate; and a fourth plate overthe second substrate and overlapping with the second plate.
 9. Thedisplay device according to claim 2, comprising an integrated circuit(IC) chip mounted on the FPC, the IC chip comprising: a signal linedriver circuit electrically connected to the display portion.
 10. Adisplay device comprising: a display panel comprising: a first plate anda second plate; a first substrate over the first plate and the secondplate, the first substrate having flexibility; a display portion overthe first substrate, the display portion comprising: a transistor; and adisplay element electrically connected to the transistor; a first drivercircuit over the first substrate and overlapping with the first plate;and a second substrate over the display portion and the first drivercircuit, the second substrate having flexibility; and an integratedcircuit (IC) chip mounted on an end portion of the display panel, the ICchip comprising: a signal line driver circuit electrically connected tothe display portion, wherein the end portion of the display panel isalong a first direction, wherein the display portion is bendable betweenthe first plate and the second plate, wherein the display portion isbendable along the first direction, wherein the first driver circuit isprovided along a second direction perpendicular to the first direction,and wherein the first plate and the second plate are attached to thesame surface of the first substrate.
 11. The display device according toclaim 10, comprising a supporting portion at the end portion of thedisplay panel, wherein the FPC is provided in the supporting portion.12. The display device according to claim 10, wherein the displayelement is a light-emitting element.
 13. The display device according toclaim 10, wherein the display element is a liquid crystal element. 14.The display device according to claim 10, wherein the display element isan electrophoretic display element.
 15. The display device according toclaim 10, wherein the first plate and the second plate are reinforcingplates.
 16. The display device according to claim 10, comprising: athird plate over the second substrate and overlapping with the firstplate; and a fourth plate over the second substrate and overlapping withthe second plate.
 17. A display device comprising: a display panelcomprising: a first plate and a second plate; a first substrate over thefirst plate and the second plate, the first substrate havingflexibility; a display portion over the first substrate, the displayportion comprising: a transistor; and a display element electricallyconnected to the transistor; a first driver circuit over the firstsubstrate and overlapping with the first plate; and a second substrateover the display portion and the first driver circuit, the secondsubstrate having flexibility, wherein the display portion is bendablebetween the first plate and the second plate, wherein the displayportion is bendable along a first direction, wherein the first drivercircuit is provided along a second direction perpendicular to the firstdirection, wherein the first plate and the second plate are attached tothe same surface of the first substrate, and wherein an operationportion is provided for the display panel so that the display portion iscapable of functioning as a touch display.
 18. The display deviceaccording to claim 17, comprising a supporting portion at an end portionof the display panel, wherein the FPC is provided in the supportingportion.
 19. The display device according to claim 17, wherein thedisplay element is a light-emitting element.
 20. The display deviceaccording to claim 17, wherein the display element is a liquid crystalelement.
 21. The display device according to claim 17, wherein thedisplay element is an electrophoretic display element.
 22. The displaydevice according to claim 17, wherein the first plate and the secondplate are reinforcing plates.
 23. The display device according to claim17, comprising: a third plate over the second substrate and overlappingwith the first plate; and a fourth plate over the second substrate andoverlapping with the second plate.
 24. The display device according toclaim 17, wherein the operation portion is provided with a keyboard oran operation button.
 25. A display device comprising: a display panelcomprising: a first plate and a second plate; a first substrate over thefirst plate and the second plate, the first substrate havingflexibility; a display portion over the first substrate, the displayportion comprising: a transistor; and a display element electricallyconnected to the transistor; a first driver circuit over the firstsubstrate and overlapping with the first plate; and a second substrateover the display portion and the first driver circuit, the secondsubstrate having flexibility; and a flexible printed circuit (FPC)attached to an end portion of the display panel, wherein the end portionof the display panel is along a first direction, wherein the displayportion is bendable between the first plate and the second plate,wherein the display portion is bendable along the first direction,wherein the first driver circuit is provided along a second directionperpendicular to the first direction, wherein the first plate and thesecond plate are attached to the same surface of the first substrate,and wherein the transistor comprising a semiconductor layer comprisingan oxide semiconductor.
 26. The display device according to claim 25,comprising a supporting portion at the end portion of the display panel,wherein the FPC is provided in the supporting portion.
 27. The displaydevice according to claim 25, wherein the display element is alight-emitting element.
 28. The display device according to claim 25,wherein the display element is a liquid crystal element.
 29. The displaydevice according to claim 25, wherein the display element is anelectrophoretic display element.
 30. The display device according toclaim 25, wherein the first plate and the second plate are reinforcingplates.
 31. The display device according to claim 25, comprising: athird plate over the second substrate and overlapping with the firstplate; and a fourth plate over the second substrate and overlapping withthe second plate.
 32. The display device according to claim 25,comprising an integrated circuit (IC) chip mounted on the FPC, the ICchip comprising: a signal line driver circuit electrically connected tothe display portion.
 33. The display device according to claim 25,wherein the oxide semiconductor comprises indium and zinc.
 34. A displaydevice comprising: a display panel comprising: a first plate and asecond plate; a first substrate over the first plate and the secondplate, the first substrate having flexibility; a display portion overthe first substrate, the display portion comprising: a transistor; and adisplay element electrically connected to the transistor; a first drivercircuit over the first substrate and overlapping with the first plate;and a second substrate over the display portion and the first drivercircuit, the second substrate having flexibility; and an integratedcircuit (IC) chip mounted on an end portion of the display panel, the ICchip comprising: a signal line driver circuit electrically connected tothe display portion, wherein the end portion of the display panel isalong a first direction, wherein the display portion is bendable betweenthe first plate and the second plate, wherein the display portion isbendable along the first direction, wherein the first driver circuit isprovided along a second direction perpendicular to the first direction,wherein the first plate and the second plate are attached to the samesurface of the first substrate, and wherein the transistor comprising asemiconductor layer comprising an oxide semiconductor.
 35. The displaydevice according to claim 34, comprising a supporting portion at the endportion of the display panel, wherein the FPC is provided in thesupporting portion.
 36. The display device according to claim 34,wherein the display element is a light-emitting element.
 37. The displaydevice according to claim 34, wherein the display element is a liquidcrystal element.
 38. The display device according to claim 34, whereinthe display element is an electrophoretic display element.
 39. Thedisplay device according to claim 34, wherein the first plate and thesecond plate are reinforcing plates.
 40. The display device according toclaim 34, comprising: a third plate over the second substrate andoverlapping with the first plate; and a fourth plate over the secondsubstrate and overlapping with the second plate.
 41. The display deviceaccording to claim 34, wherein the oxide semiconductor comprises indiumand zinc.
 42. A display device comprising: a display panel comprising: afirst plate and a second plate; a first substrate over the first plateand the second plate, the first substrate having flexibility; a displayportion over the first substrate, the display portion comprising: atransistor; and a display element electrically connected to thetransistor; a first driver circuit over the first substrate andoverlapping with the first plate; and a second substrate over thedisplay portion and the first driver circuit, the second substratehaving flexibility, wherein the display portion is bendable between thefirst plate and the second plate, wherein the display portion isbendable along a first direction, wherein the first driver circuit isprovided along a second direction perpendicular to the first direction,wherein the first plate and the second plate are attached to the samesurface of the first substrate, wherein an operation portion is providedfor the display panel so that the display portion is capable offunctioning as a touch display, and wherein the transistor comprising asemiconductor layer comprising an oxide semiconductor.
 43. The displaydevice according to claim 42, comprising a supporting portion at an endportion of the display panel, wherein the FPC is provided in thesupporting portion.
 44. The display device according to claim 42,wherein the display element is a light-emitting element.
 45. The displaydevice according to claim 42, wherein the display element is a liquidcrystal element.
 46. The display device according to claim 42, whereinthe display element is an electrophoretic display element.
 47. Thedisplay device according to claim 42, wherein the first plate and thesecond plate are reinforcing plates.
 48. The display device according toclaim 42, comprising: a third plate over the second substrate andoverlapping with the first plate; and a fourth plate over the secondsubstrate and overlapping with the second plate.
 49. The display deviceaccording to claim 42, wherein the operation portion is provided with akeyboard or an operation button.
 50. The display device according toclaim 42, wherein the oxide semiconductor comprises indium and zinc.